Nitrogen enrichment delays the emergence of an aridity-induced threshold for plant biomass

Abstract Crossing certain aridity thresholds in global drylands can lead to abrupt decays of ecosystem attributes such as plant productivity, potentially causing land degradation and desertification. It is largely unknown, however, whether these be altered by other key change drivers known affect the water-use efficiency productivity vegetation, elevated CO2 nitrogen (N) enrichment. Using > 5000 empirical measurements biomass, we show that crossing an (1–precipitation/potential evapotranspiration) threshold ∼0.50, which marks transition from dry sub-humid semi-arid climates, leads declines aboveground biomass (AGB) progressive increases root: shoot ratios, thus importantly affecting carbon stocks their distribution. N enrichment significantly increased AGB delayed emergence its 0.49 0.55 (P < 0.05). By coupling remote sensing estimates leaf area index with simulations multiple models, found did not alter observed threshold. 2100, under RCP 8.5 scenario, forecast a 0.3% net increase exceeding detected scenario includes enrichment, comparison 2.9% if effect considered. Our study indicates could mitigate great extent negative impact increasing on drylands. These findings are critical for improving forecasts vegetation changes response ongoing environmental change.